The present invention relates to a method and apparatus for gas chromatography. More particularly, the invention relates to an electrolyzer-operated gas-cylinder-free gas chromatograph having a flame ionization detector (GC-FID).
Gas chromatography (GC) is a widely used analytical technology that is finding a growing number of applications in the analysis of volatile and semi-volatile compounds. Among the several currently available GC detectors, the flame ionization detector (FID) is the detector most widely used and for the broadest range of applications. The FID is based on the combustion of organic compounds that elute from the GC column in a hydrogen diffusion air flame and the consequent production of charged species from the combustion of the organic compounds. The FID is a highly successful detector due to its robustness, high reliability, high sensitivity, universal carbon-selective detection capability, broad linear dynamic range, fast response, high temperature operation capability and excellent reproducibility. As a result, the FID has become the GC industry""s standard detector of choice.
However, both the GC and FID suffer from the major limitation of requiring several high quality gases. This limitation impairs the GC""s operational safety, severely limits its transportability and usage outside the laboratory, considerably increases its cost of purchase and use, and reduces its ease of use. As a result, portable GC""s are mostly used with a thermal conductivity detector (TCD) that is less sensitive than the FID, suffers from limited temperature operation capability and is subjected to water interference. An alternative detector is the photo ionization detector (PID); however, the PID is too selective for many applications and is not semi-quantitative; it thus is incapable of properly analyzing several important compounds, such as methane or acetone.
A new type of FID has been developed, based on the use of a water electrolyzer, for the production of an unseparated, premixed, oxygen and hydrogen combustible gas mixture. This electrolyzer-powered FID (EFID) is based on a premixed, stoichiometric oxygen and hydrogen flame with a relatively low flow rate of the combustible gas mixture. In addition to a different EFID flame, its operation further requires the reduction of the flame tip diameter to prevent flame flashbacks and the heating of the FID gas exit to avoid water condensation. The EFID, despite its different flame chemistry, serves as a carbon-selective detector like the FID and maintains all the advantages of the FID listed above, with the addition of slightly increased sensitivity. The same EFID electrolyzer has also been used for the operation of a nitrogen and phosphorus detector.
The use of the EFID renders superfluous the use of hydrogen and air gas cylinders in the GC. It also considerably reduces the helium carrier gas consumption, since no helium make-up gas is required for optimal operation of the EFID. However, an inert carrier gas, such as helium, nitrogen or hydrogen, is still required for the operation of the GC injector and as a carrier gas for the analytical separation column. The common perception is that oxygen must be avoided, as it destroys the GC separation column. Furthermore, oxygen is a reactive gas that can react and oxidize the sample compounds in the hot injector. Clearly, the complete removal of all of the gas cylinders from the GC remains an important challenge.
The present invention relates to a gas cylinder-free, GC-EFID system. This system is uniquely based on the use of a water electrolyzer for the provision of substantially all of the gases needed for the operation of a GC-FID system. In the system of the invention, the water electrolyzer produces a stoichiometric oxygen and hydrogen gas mixture. The mixture is used as is, without oxygen removal or any gas separation, as the gas needed for the purge and trap injection system, as the carrier gas in the analytical separation capillary column and as the single gas supply source of the EFID. The result is a gas cylinder-free GC-EFID system having only liquid water as a consumable material and that releases only water vapor into the environment at the small rate of about 10 mg/min. The present invention is based on the realization of several important advantages of water electrolysis as a method for the provision of the total gas supply of gas chromatography systems:
1) Water is a safe, non-toxic, environmentally friendly material.
2) Water is a liquid in abundant, easy, low-cost supply.
3) Water provides, upon its electrolysis, a hydrogen and oxygen gas mixture having a gas volume about 2000 times larger than the volume of the water.
4) Unlike gas, water can be transported, including in airplanes, without the safety issues and constraints relating to compressed or flammable gas.
5) Water electrolysis automatically produces the necessary pressure for delivery of the required flow rate of the gases produced.
6) Water electrolysis is amenable to simple, yet accurate, electronic control of the total gas flow rate by controlling the electrolysis current. In addition, the initial stoichiometric ratio of hydrogen to oxygen in the gas mixture is also inherently ensured. Thus, the water electrolyzer replaces a costly, three-channel electronic flow control.
7) Water electrolysis produces ultra-clean gases without any organic compound impurities.
8) Water electrolysis, without subsequent gas separation, provides the ultimately reliable gas supply device with no moving parts.
9) Water electrolysis, without subsequent gas separation, provides the ultimate low energy consumption, pressurized gas source, compared with any other gas generation source.
10) Water electrolysis, with hydrogen and oxygen separation, can provide both relatively inert hydrogen gas to serve as a GC column carrier gas and oxygen for post-column mixing with the hydrogen for EFID operation.
In accordance with the present invention, there is therefore provided a gas chromatography method for analyzing materials vaporizable in a gas chromatograph system, said method comprising filling a sample injection device with a sample of the compounds to be analyzed; transferring said sample compounds into an analytical separation column with a transfer gas; passing a carrier gas inside said analytical separation column for the time separation of said sample compounds; controlling the temperature of said column for achieving separation of said sample compounds; transferring the vaporized sample compounds eluted from said column into a flame ionization detector; providing the gases required for the operation of said flame ionization detector, and analyzing the data output of said flame ionization detector for analysis of said sample compounds, characterized in that the gases required for the operation of said gas chromatograph system are produced by water electrolysis.
In addition, the invention provides a gas chromatography method for analyzing materials vaporizable in a gas chromatograph system, said method comprising filling a sample injection device with a sample of the compounds to be analyzed; transferring said sample compounds into an analytical separation column with a transfer gas; passing a carrier gas inside said analytical separation column for time separation of said sample compounds; controlling the temperature of said column for achieving separation of said sample compounds; transferring the vaporized sample compounds eluted from said column into a detector; providing the gases required for the operation of said detector, and analyzing the data output of said detector for analysis of said sample compounds, characterized in that the gases required for the operation of said gas chromatograph system are produced by water electrolysis without separating the hydrogen from the co-produced oxygen.
The invention further provides a gas chromatograph system for analyzing vaporizable materials, said system comprising means for filling a sample injection device with a sample of the compounds to be analyzed; means for transferring said sample compounds with a transfer gas into an analytical separation column; means for passing a carrier gas inside said analytical separation column for the time separation of said sample compounds; temperature control means for controlling the temperature of said column for achieving separation of said sample compounds; means for transferring vaporized sample compounds eluted from said column into a flame ionization detector for subsequent detection; means for providing the gases required for the operation of said flame ionization detector, and means for analyzing output data of said flame ionization detector for analysis of said sample compounds, characterized in that the gases required for the operation of said gas chromatograph system are provided by a water electrolyzer.
The invention still further provides a gas chromatograph system for analyzing vaporizable materials, said system comprising means for filling a sample injection device with a sample of the compounds to be analyzed; means for transferring said sample compounds with a transfer gas into an analytical separation column; means for passing a carrier gas inside said analytical separation column for time separation of said sample compounds; temperature control means for controlling the temperature of said column for achieving separation of said sample compounds; means for transferring vaporized sample compounds eluted from said column into a detector for subsequent detection; means for providing the gases required for the operation of said detector, and means for analyzing output data of said detector for analysis of said sample compounds, characterized in that the gases required for the operation of said gas chromatograph system are provided by a water electrolyzer without separating the hydrogen from the co-produced oxygen.
The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that. it may be more fully understood.
With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.